CURLWP global register in NetBSD/mips

["Toru Nishimura" <locore64%alkyltechnology.com@localhost>]

Guys,

NetBSD/mips kernel uses a dedicated register to hold curlwp
global variable.  Register S7 is used in -current whileT8 in
matt-nb5-mips64 branch (why differ?)

The place where curlwp register is reassigned is pretty
limited.  As far as I understand, only cpu_switchto() does it.

Looking at cpu_lwp_fork() bottom half, we find a sequence
to assign values for newlwp's switchframe.  The following line

 pcb->pcb_context.val[MIPS_CURLWP_LABEL] = (intptr_t)l2;

is supposed to make the dedicated curlwp register to hold
newlwp at the very bottom of cpu_switchto().

During the context switch steps, cpu_switchto() assigns newlwp
value to the reserved register anyway.  So, this particular
switchframe arrangement for cpu_switchto() bottom makes little
sense.

Now I propose here;

1. remove [... _CURLWP_LABEL] arrangement in vm_machdep.c
2. remove S7 (T8) value restoration at the bottom of cpu_switchto().

Comments are welcome.

Toru Nishimura / ALKYL Technology